In the middle of November 1915, Albert Einstein was hard at work. He would later say he never labored more intensely than he did that autumn. Since the beginning of October, he'd been wrestling with what would become his greatest discovery, what we now call the General Theory of Relativity, a theory of gravity that said our universe is one in which space and time bend, warped by all the matter and energy it contains. It was a genuinely revolutionary conception, and it would, on its public confirmation four years later, transform Einstein into the first true celebrity of science.
But in the week between November 11 and 18, the problem that occupied him in that second year of what was already being called "the Great War" seemed simple, even trivial: retracing the orbit of the planet nearest our sun, fleet-footed Mercury. More precisely, could his brand-new mathematical approach account for a wobble in that orbit that had been noticed and unexplained for half a century?
The effect was tiny — on the order of one part in 10,000. But it was — and is — really there. The anomaly had lingered for decades, an embarrassment to astronomers. That ended the moment Einstein worked through the last line of his calculation. There, as he put it in the formal language required of proper scientific communication, "The calculation for the planet Mercury yields a perihelion advance of 43 arc minutes per century, while the astronomers assign 45" +/- 5" per century as the unexplained difference between observations and the Newtonian theory." Belaboring the obvious, he added, "This theory therefore agrees completely with the observations."
In private, he let himself go. As the correct answer appeared, he told a friend, his heart actually shuddered in his chest — genuine palpitations. He wrote ...